TYING DEVICE IN WHICH THE DRIVE MEANS ARE ELECTRIC SERVOMOTORS

Abstract: A device for tying objects with wire, for example bales of fiber material. The device comprises a feed unit (11) for feeding and tightening the wire (12), an openable rail (14, 16) for guiding the wire around the object, a unit (17) for locking the wire end, a unit (18) for twisting a wire knot, a cutting unit (19) and a unit (20) for pushing out the knot. The drive means for the units for wire feed (11) and, respectively, twisting (18) are electric servomotors (24 and, respectively, 29).

Description: Tying device in which the drive means are electric servomotors This invention relates to a.device for tying objects with wire, for example bales of fiber material. Pulp bales are tied both individually and in the form of stacked units comprising a certain number of bales, normally six or eight. Such a unit load has a weight of between one and two tons. The strength of the wire connection binding together the unit load, therefore, is very important from a safety aspect, because several persons can stand close to the load at its lifting by means of wires. The equipment used for twisting the knot in a tied loop as well as the knot itself, therefore, is subject to very compre¬ hensive safety regulations and accurate safety control. The tying device comprises a unit for feeding the wire through an openable wire guide rail around the object. The feed is also used for tightening the wire.There is further used a twisting member, which comprises a unit for locking the wire end, a unit for twisting a wire knot, a cutting unit and a unit for pushing out the knot. The wire guide rail extends about the object to be tied and guides the wire at its feed. The wire is fed through the twisting member about the object of tying. When the free end of the wire arrives at the twisting member for the second time, the wire is stopped and retained in the locking unit, whereafter it is tightened by re¬ versing the feed unit. The wire guide rail is thereby opened, and the wire is drawn around the object to be tied, the knot is twisted, the wire is cut and pushed out of the twisting member. The different units normally are driven and controlled hydraulic- ally by motors and cylinders. It was found that this drive system fails to work with the precision desired at the tying. Ample margins, therefore, are required to ensure its proper functioning, especially at wire feeding, wire tightening and twisting. This implies also that the wire can be subjected to such stresses at the tying, that the wire must be designed thicker than required for holding the tied objects together. The hydraulic motors, further¬ more, require relatively complicated and bulky hydraulic assemblies, which imply the risk of functional disorder and high service costs. The present invention offers a solution for the aforesaid problems by using electric servomotors. The characterizing features of the invention are apparent from the attached claims. The invention is described in greater detail in the following by way of an embodiment thereof and with reference to the accompany¬ ing drawings, in which Fig. 1 shows a tying device according to the invention, Fig. 2 shows the twisting member in the tying device, Fig. 3 shows a pneumatic/hydraulic system for controlling the different units in the tying device. The tying device is of the type shown and described in the patent publication SE 380496. The tying device comprises a stand 10, on which the different units are arranged. A feed unit 11 feeds tying wire 12 from a wire magazine around the object to be tied 13 and thereafter tightens the wire. A wire guide rail 14 extends about the object of tying 13. A twist¬ ing member 15 comprises a guide rail 16 for guiding the wire through the twisting member 15, a unit 17 for locking the wire end, a unit 18 for twisting a wire knot, a unit 19 for cutting the wire and a unit 20 for pushing out the finished twisted knot. The entire tying device preferably is movable so that it can be placed in a conveying track for the objects to be tied and be easily replaced when required. The feed unit 11 comprises a guide wheel 21, about which the wire 12 runs, and a driven feed wheel 22, to which at least one counter- -pressure roll 23 abuts. The feed wheel 22 is driven by a first el¬ ectric servomotor 24. The wire guide rail 14 is openable and provided with grooves for the wire 12. During the wire feed, the rail 14 is held in closed position by means of preferably pneumatic piston/cylinder units 40. At the tightening of the wire, the wire guide rail 14 is opened by the piston/cylinder units 40. The tying member 15 is exchangeable and detachably attached to the drive means for the units 16-20 comprised in the tying member. The drive means are spring-loaded single-acting piston/cylinder units 25-28, which actuate the guide rail 16, locking unit 17, cutting unit 19 and push-out unit 20 as well as a second electric servomotor. 29, which actuates the twisting roll 31 of the twist¬ ing unit 18 via pinions 30. The piston/cylinder units 25,28, which actuate the guide rail 16 and push-out unit 20, preferably are included in a pneumatic system, while the piston/cylinder units 26,27, which actuate the units 17,19 for locking and cutting, preferably are included in a combined pneumatic/hydraulic system. In this combined system the piston/ cylinder units 26,27 are directly actuated hydraulically from a pneumatically actuated power amplifying hydraulic cylinder 32. Hereby the hydraulic system is minimized at maintained power and safety. At the wire feed, the feed unit 11 is driven by the first electric servomotor 24 through a predetermined number of revolutions, so that a definite wire length is fed around the object of tying 13 and the wire end arrives at the locking unit 17. The length of the wire feed 12 is counted from the wire end passing an indicat¬ or 33 at the in-feed. The wire end is retained in the locking unit 17. The wire is thereafter tightened by reversing the servomotor 24 of the feed unit 11 until the wire has been tightened down onto the object of tying 13 and the necessary torque in the servomotor 24 has been obtained. After the predetermined torque for the wire tightening has been achieved and been maintained for a short time, the second electric servomotor 29 starts for driving the twisting roll 31 of the twisting unit 18. The rotation of the servomotor 29 is controlled so that the twisting roll 31 first is rotated through a predeterm¬ ined number of revolutions and an additional angle and thereafter is reversed through the same angle. Hereby a certain over-twisting is obtained, which compensates for the spring back of the wire knot. When the twisting is completed, the wire is cut in the cutting unit 19, and the push-out unit 20 ensures that the knot leaves the tying member 15. After its cutting, the wire is pulled back by the feed unit 11 past the indicator 13, and the device is ready for a new tying operation. By using electric servomotors for driving the feed unit and twist¬ ing unit, it is possible to accurately control the wire feed, wire tightening and twisting. The number of revolutions and the angle position of the servomotors can be indicated, for example, by pulse metering or in some other way. Speed, acceleration and retardation of the servomotors can be controlled so that jerks and jolts in the wire are avoided. It was found possible accord¬ ing to the invention to reduce the wire diameter at maintained functional safety, compared with conventional equipment, for example from 2,3 mm to 2 mm. In addition to the indication equipment mentioned above, trans¬ mitters can be positioned in different places for indicating the position of the wire and movable parts of the different units. Such an arrangement can be utilized advantageously, for example, for functional information and trouble finding. The invention, of course, is not restricted to the embodiment shown and described, but can be varied within the scope of the invention idea.

Claims: Claims 1. A device for tying objects with wire, comprising a feed unit (11) for feeding and tightening the wire (12) , an openable rail (14,16) for guiding the wire around the object, a unit (17) for locking the wire end, a unit (18) for twisting a wire knot, a cutting unit (19) and a unit (20) for pushing out the knot, c h a r a c t e r i z e d i n that the drive means for the units for wire feed (11) and, respectively, twisting (18) are electric servomotors (24 and, respectively, 29). 2. A device as defined in claim 1, c h a r a c t e r i z e d i n that an indicator (33) is provided for indicating the position of the wire end before the tying. 3. A device as defined in claim 1 or 2, c h a r a c t e r ¬ i z e d i n that the servomotors (24,29) are arranged to rotate through a predetermined number of revolutions for the wire feed and wire tightening and, respectively, wire twisting. 4. A device as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that a pneumatic system is provided to control the openable guide rail (14,16) and the unit (20) for pushing out the wire knot, and a combined pneumatic/hydraulic system is provided to control the units for wire locking (17) and wire cutting (19) . 5. A device as defined in any one of the preceding claims, c h a r a c t e r i z e d i n that transmitters are posit¬ ioned in a plurality of positions for indicating the position of the wire and the setting of the different units.

Inventors: JONSSON AGE, JONSSON, AGE
Applicants: JONSSON AGE, SUNDS DEFIBRATOR IND AB, JONSSON, AGE, SUNDS DEFIBRATOR INDUSTRIES AB
Application year: 1994
Main classification: B65B13
IPC codes: B65B13